DC power control of switching devices

ABSTRACT

A system for controlling the connection of power from a main supply (11) to electrical devices (22) by way of switching devices (19). The system includes a low voltage, direct current power supply (10), a plurality of command units (15) connected to and powered from the power supply by way of an electrical connection (14), and a plurality of switching devices (19) connected to and powered from the power supply by way of the electrical connection (14). Each of the command units (15A, 15B and 15C) is arranged to generate a uniquely coded pulse-form command signal to a central processing unit (18) by way of the electrical connection (14), and the central processing unit is arranged to generate pulse-form actuating signals having codes determined by the command signals. The central processing unit is arranged to feed the actuating signals to the switching devices (19) by way of the electrical connection (14). The power supply (10) incorporates a voltage regulator (11) which includes circuitry which functions to detect the presence of the pulse-form signals on the electrical connection (14), and the voltage regulator includes means for modulating the output voltage of the power supply between two discrete levels responsive to and at a rate corresponding with that of the pulse-form signals.

FIELD OF THE INVENTION

This invention relates to a system for controlling actuation of mainpowered electrical devices, using a low voltage, direct current controlcircuit to command and effect switching of power to the devices. Theinvention has been developed and is hereinafter described by way ofexample in the context of a system that utilizes a central processorwhich is arranged to act on command signals and issue actuating signalsfor the purpose of switching power to devices in a domestic residence orother building.

BACKGROUND OF THE INVENTION

In a system to which the invention relates, common control circuitwiring is employed to carry command signals, actuating signals andcurrent at a level sufficient to effect actuation of switching relays.This approach minimizes the amount of wiring required for a given systeminstallation but it does impose a requirement for voltage regulation inorder that reliable operation will occur with changing circuitconditions, including changes to the size of the installation. Theinclusion of a voltage regulated, direct current power supply as suchdoes not present any difficulties, but a problem occurs when attemptingto modulate the otherwise constant control circuit voltage with commandand/or actuating signals. That is, a conventional regulated power supplywill present zero impedance to an alternating signal and, thus,effectively absorb the command and actuating signals.

One attempt has been made to avoid this problem by arranging for theresponse time of voltage regulation to be slow relative to the frequencyof modulation used by both the command and the actuating signals.However, this solution requires the introduction of R.C time constantcircuit components, resulting in consequential power loss and imposinglimits on the number of load devices that may be connected to a giveninstallation.

DESCRIPTION OF THE INVENTION

The present invention seeks to avoid this problem, without increasingthe amount of control circuit wiring, by arranging for the controlcircuit voltage to be regulated between two levels at the modulationrate of the control and actuating signals.

Thus, the present invention may be defined broadly as providing a systemfor controlling the connection of power to electrical devices by way ofswitching devices and which comprises a low voltage, direct currentpower supply, an electrical connection between the power supply and theswitching devices, and means for generating and feeding to theelectrical connection pulse-form control signals. The system ischaracterized in that the power supply includes means for detecting thepresence of the pulse-form control signals and means for modulating theoutput voltage of the power supply between two discrete levelsresponsive to and at a rate corresponding with that of the pulse-formcontrol signals.

The invention in a more specific, preferred form may be defined asproviding a system for controlling the connection of power to electricaldevices by way of switching devices and which comprises a low voltage,direct current power supply, a plurality of command units connected toand powered from the power supply by way of an electrical connection,and a plurality of switching devices connected to and powered from thepower supply by way of the electrical connection. Respective ones of thecommand units are arranged to generate uniquely coded pulse-form commandsignals and to feed the command signals to a central processing unit byway of the electrical connection, and the central processing unit isarranged to generate pulse-form actuating signals having codesdetermined by respective command signals and to feed the actuatingsignals to the switching devices by way of the electrical connection.The system is characterized in that the power supply incorporates avoltage regulator which includes means for detecting the presence of thepulse-form signals and means for modulating the output voltage of thepower supply between two discrete levels responsive to and at a ratecorresponding with that of the pulse-form signals.

The two discrete output voltage levels of the power supply comprise anupper level which corresponds to the unmodulated voltage level of thesupply and a lower level corresponding to the minimum voltage levelrequired for the command and/or actuating signals. The upper voltagelevel will typically be in the order of 15 to 30 volts, and thedifference between the upper and lower voltage levels will typically bein the order of one to five volts.

In use of the above defined system (when in its preferred form) theswitching devices are arranged to effect connection of power toassociated ones of the electrical devices responsive to detection by theswitching devices of appropriately coded actuating signals.

PREFERRED FEATURES OF THE INVENTION

The command units preferably comprise signal generators that producedigital form coded signals when operated. Operation may be effectedmanually, for example by operation of a push-button type switch, orremotely from a further signal generator such as an infra-red signalradiating device.

The switching devices preferably comprise electromagnetic relays havingcontacts which are either normally open or normally closed, dependingupon the electrical devices to which the relays are required to switchpower. Alternatively, the switching devices may comprise bistable relayunits. In either case, each of the switching relays includes circuitrywhich is arranged to detect for the existence of an appropriately codedactuating signal from the central processing unit and to initiate aswitching operation upon detection of the appropriate actuating signal.

The central processing unit may comprise any conventional type ofstand-alone processor or computer and it preferably incorporates akeyboard or other mechanism to permit data entry and, possibly,programming of the system to meet specific operational requirements.

The system may be operated at various levels of complexity, and at thesimplest level the system may be employed to control energization ofpredetermined room lighting responsive to manual activation of one ormore switch-operated command units. Again at a simple level, the systemmay be programmed to control energization of predetermined internaland/or external lighting and to arm an intruder alarm in the event thata mobile target is detected to be present by command units in the formof proximity detectors. As a further example, the system may beprogrammed to effect energization of lighting and other electricaldevices at predetermined times, either for the purpose of readying adwelling for intending occupancy or to give the impression ofresidential occupation to would-be intruders. Override controls may beprogrammed into the system, for example to prevent energization oflighting under high ambient light conditions or to bar actuation ofselected electrical devices.

The invention will be more fully understood from the followingdescription of a preferred embodiment of a system for controlling theactuation of mains powered electrical devices in a domestic residence.The description is provided with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings

FIG. 1 shows a schematic representation of the complete system,

FIG. 2 shows a circuit diagram of a power supply that is incorporated inthe system of FIG. 1,

FIG. 2A is a graphical representation of an example output voltage ofthe power supply, and

FIG. 3 shows a diagrammatic representation of a signal generator whichis incorporated in a command unit in the system of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

As illustrated, the complete control system comprises a power supply 10which is connected to a single phase, alternating current main supply11. The power supply incorporates a transformer/bridge rectifier circuit12, as shown in FIG. 2, and it provides a direct current output to avoltage regulator 13. The output from the voltage regulator ismaintained at a nominal potential of 20 volts and is connected totwo-wire control circuit wiring 14.

Three command units 15A, B and C are shown connected to the controlcircuit wiring 14, although a typical system would normally employ asignificantly greater number of command units. Each command unit 15incorporates a manually operable push-button type switch 16 and a signalgenerator 17. The signal generator associated with each command unit 15is shown in FIG. 3, is powered by way of the control circuit wiring 14and is arranged to generate a unique command signal composed of adigital modulation of the control circuit voltage.

The command signals from the command units 15 are detected by a centralprocessing unit 18 which is connected to the control circuit wiring 14and powered from the main supply 11. The central processing unit 18 isprogrammed to translate detected command signals into actuating signalswhich are fed to the control circuit wiring for detection by actuatorrelay units 19A, B and C. The central processing unit is programmed topreclude simultaneous superimposition of two or more command and/oractuating signals on the control circuit wiring.

Also, the central processing unit 18 includes programming facilitieswhich permit local programming or reprogramming of the system, using akeyboard (not shown), to effect extension of the system and/or to modifythe translating functions of the central processing unit.

The actuator relay units 19 each incorporate a bistable relay 20 anddetector/signal processing circuitry 21, the latter of which is arrangedto detect for an appropriately coded actuation signal from the centralprocessing unit 18 and to apply a relay operating signal to theassociated relay 20 upon receipt of the actuating signal. Having beenactuated to a closed condition, each relay 20 functions to connect anassociated load 22 to the main supply 11.

As an example of one possible operating condition of the system,operation of the switch 16 in command unit 15A may produce a commandsignal having a code which is recognised by the central processing unit18 as one which should be translated into an actuating signal which isdetectable by relay unit 19C. Then, having detected the actuatingsignal, the relay unit 19C causes its relay 20 to close in order thatmain power will be connected to load 22C.

The power supply shown in FIG. 2 functions to maintain the 20 voltsupply to the control circuit wiring 14 in the absence of any command oractuating signal on the control circuit wiring 14. For this purpose thepower supply circuit incorporates a voltage regulator 22. To protectagainst "absorption" of the command or actuating signals, as aconsequence of normal voltage regulation performed by the power supply,the power supply as shown in FIG. 2 is arranged to regulate or,expressed in an alternative way, modulate the output voltage to thecontrol circuit wiring 14 between two levels at a rate which correspondswith that of the coded command and actuating signals that appear at anyone time on the control circuit wiring. Thus, the power supply functionsto detect for the presence of pulse-form signals generated by thecommand units 15 or by the central processing unit 18 and to modulatethe supply voltage applied to the same control circuit wiring 14 onwhich the signals appear. Modulation of the supply voltage occursresponsive to the existence of a command or actuating signal and at arate corresponding with that of the coded command or actuating signal.Thus, the supply voltage is modulated between the two (upper and lower)levels and in a manner which emulates the codes of the command oractuating signals. The upper level of the power supply voltage is +20volts, as stated above, and the lower level is typically +17 volts asshown in the voltage signal that is graphed in FIG. 2A.

The voltage regulator 22 comprises an LM350 adjustable linear voltageregulator and its output level is determined by the value of theresistance ratio R₂ /R₁ or, when a comparator 23 is controlledeffectively to place resistance R₂ and R₃ in parallel, by the resistanceratio R₂.R₃ /R₁ (R₂ +R₃).

With the specific circuit configuration shown in FIG. 3 and with thevalue of the output voltage being determined by the resistance ration R₂/R₁, the output voltage is maintained at a level of 20 volts with nocommand or actuator signals on the control circuit wiring 14.

The comparator 23 comprises an operational amplifier having a smalloffset, determined by the ratio R₄ /R₅ and, because of the small offset,a separate regulated voltage source 24 is provided to ensure a constantvoltage supply to the comparator circuit 23. The regulator 24 comprisesa 78L12 constant voltage supply integrated circuit device.

When the system is operating without command or actuator signals on thecontrol circuit wiring 14, the non-inverting input of the comparator 23remains high and the output voltage level of the regulator 22(determined by the resistance ratio R₂ /R₁) is maintained high at 20volts. However, if one of the command units as shown in FIG. 3 isactuated, current flow through the collector resistor R₆ in the signalgenerator 17 will be detected as current flow through resistor R₇ in thepower supply circuit of FIG. 2. As a consequence and as a result of thelow offset established by the value of resistors R₄ and R₅, theinverting input to the comparator 23 will go high relative to thenon-inverting input, cause the output of the comparator to go low andeffectively place resistor R₃ in parallel with resistor R₂. The outputof the regulator 22 will then go low, with the circuit component valuesindicated to a level of approximately 17 volts.

The regulator output voltage will stay low until current flow throughresistors R₆ and R₇ ceases, whereupon the regulator output will returnto the high level. The same circuit operation will occur with generationof an actuator signal in the system.

I claim:
 1. A system for controlling the connection of power toelectrical devices by way of electrically actuated switching devices andwhich comprises:a low voltage, direct current power supply for theswitching devices, an electrical connection between the power supply andthe switching devices, a plurality of actuatable command units connectedin circuit with the electrical connection and arranged to generate andfeed digitally coded pulse-form control signals to the electricalconnection; a central processing unit connected in circuit with theelectrical connection and arranged to detect the control signals, togenerate digitally coded pulse-form actuating signals in response toreceipt of the control signals and to feed the actuating signals to theelectrical connection; the switching devices being arranged to effectswitching operations responsive to detection of the presence ofpredetermined ones of the digitally coded actuating signals on theelectrical connection; and the power supply incorporating means fordetecting changes in the current flow in the electrical connectionresulting from the presence of the pulse-form control signals and meansfor modulating the output voltage of the power supply between twodiscrete levels responsive to and at a rate corresponding with that ofchanges in the current flow attributable to the pulse-form signals. 2.The system as claimed in claim 1 wherein the central processing unit isprogrammed to translate respective ones of detected said command signalsinto predetermined said actuating signals.
 3. The system as claimed inclaim 1 wherein the central processing unit is programmed to precludesimultaneous superimposition of two or more command and/or actuatingsignals on the electrical connection between the power supply and theswitching devices.
 4. The system as claimed in claim 1 wherein each ofthe command units comprises a manually operable switch and means forgenerating the digitally coded command signal responsive to actuation ofthe switch.
 5. The system as claimed in claim 1 wherein the switchingdevices comprise electromagnetic relays which are arranged to connect amain supply to the electrical devices.
 6. The system as claimed in claim1 wherein the power supply is arranged to provide an output having anupper voltage level in the absence of any said pulse-form signal on theelectrical connection between the power supply and the switchingdevices, and in that the power supply is arranged to effect a reductionin the voltage level of the output responsive to and at the rate of anysaid pulse-form signal that is detected to exist on the electricalconnection.